How to change the colour of Mii outfits

Your online Smash Tag name is based on your user profile's nickname in the Switch’s system settings.

To change your nickname, go to the home menu and open System Settings. Scroll down to "Users" and select your profile. Select the "Nickname" option to pick a new name.

Note: If you change nicknames while Smash Bros is open, your new name will be applied after closing and relaunching the game.

You can change Pokemon Trainer's starter from the character select screen by clicking the Pokemon in the top-right corner of the trainer's portrait. Alternatively, as scohe001 mentioned, you can also press Y to swap pokemon.

As for your second question, there is unfortunately no way to disable Pokemon cycling on death. It will always cycle between Squirtle, Ivysaur, and Charizard when you respawn.

That being said, the longer you wait on the floating platform after you respawn, the shorter your invincibility period will be. So if you're trying to switch back to your previous Pokemon, I'd strongly suggest getting back into the game as soon as possible to make use of a longer invincibility period to switch.

Via scohe001